Environmental Hazards and Human Health

Core Case Study: Mercury’s Toxic Effects All mercury compounds are toxic One third in the atmosphere comes from natural sources Human activities provide the rest Two main human exposures Fish contaminated with mercury Inhalation of vaporized mercury Greatest risk is brain damage

Risks Are Usually Expressed as Probabilities Probability of suffering harm from a hazard Expressed as ratio or percentage Risk assessment Using statistical methods to estimate harm Risk management Deciding whether and how to reduce a particular risk

We Face Many Types of Hazards Hazard = anything that can cause: Injury, disease, death Damage to personal/public property Deterioration or destruction of environment Biological Pathogen – an organism that causes disease in other organisms Chemical Harmful chemicals Natural Fire, earthquakes, volcanoes, etc. Cultural Unsafe working conditions, poverty, etc. Lifestyle choices Smoking, drinking too much alcohol, etc.

Some Diseases Can Spread from One Person to Another The most serious biological hazards we face are infectious diseases such as flu, AIDS, tuberculosis, diarrheal diseases, and malaria Infectious disease Pathogen invades the body and multiplies Viruses, bacteria, parasites

Some Diseases Can Spread from One Person to Another Nontransmissible disease Not caused by living organisms Heart disease, most cancers, diabetes Epidemic (ex. Current flu) Large-scale outbreak of an infectious disease Pandemic – global Transmissible disease Contagious or communicable disease Infectious disease transmitted between people

Case Study: The Growing Global Threat from Tuberculosis Many people have latent TB 1.4 million deaths each year, primarily in less- developed countries Why is tuberculosis on the rise? Not enough screening and control programs Genetic resistance to a majority of effective antibiotics Person-to-person contact has increased AIDS individuals are very susceptible to TB

Viral Diseases and Parasites Kill Large Numbers of People Influenza or flu virus Kills the most worldwide HIV Infects about 2.5 million people yearly Hepatitis B virus (HBV) Emergent diseases – West Nile virus Viruses that move form animals to humans West Nile virus The new field of ecological medicine

Case Study: The Global HIV/AIDS Epidemic Acquired immune deficiency syndrome (AIDS) Caused by human immunodeficiency virus (HIV) Many secondary infections No vaccine to prevent or cure AIDS Expensive drugs – live longer 30 million deaths between 1981-2012 Kills about 1.7 million people yearly Most prevalent in sub- Saharan Africa Life expectancy dropped from 62 to 47 Alters age structure of population

Case Study: Malaria – The Spread of a Deadly Parasite Caused by parasite carried by certain mosquitoes Tropical and subtropical regions Spread Uninfected mosquito bites infected person, later bites an uninfected person Climate change – expected to spread malaria Malaria is on the rise since 1970 Drug-resistant Plasmodium Insecticide resistant mosquitoes Clearing of tropical forests AIDS patients particularly vulnerable

We Can Reduce the Incidence of Infectious Diseases Good news Percentage of worldwide deaths resulting from infectious diseases Dropped from 35% to 15% from 1970 to 2008 Vaccinations on the rise Oral rehydration therapy Bad news More money needed for medical research in developing countries

Some Chemicals Can Cause Cancers, Mutations, and Birth Defects Toxic chemicals Carcinogens Chemicals, types of radiation, or certain viruses the cause or promote cancer Mutagens Chemicals or radiation that cause mutations or increase their frequency Teratogens Chemicals that cause harm or birth defects to a fetus or embryo

Case Study: PCBs Are Everywhere – A Legacy from the Past Class of chlorine-containing compounds Very stable Nonflammable Break down slowly in the environment Travel long distances in the air Fat soluble Ends up in food chains and webs Banned, but found everywhere Part of “dirty dozen”

Some Chemicals May Affect Our Immune and Nervous Systems Some natural and synthetic chemicals in the environment can weaken and harm: Immune system Some chemicals weaken the immune system Nervous system Neurotoxins – PCBs, arsenic, lead, some pesticides

Some Chemicals Affect the Human Endocrine System Glands that release hormones that regulate bodily systems and control sexual reproduction, growth, development, learning, behavior Hormonally active agents have similar shapes and bind to hormone receptors Hormone mimics Hormone blockers

Many Factors Determine the Harmful Health Effects of Chemicals Response Acute effect – immediate or rapid Chronic effect – permanent or long- lasting Toxicology – study of harmful effects Dose Age Genetic makeup Multiple chemical sensitivity (MCS) Solubility Persistence Biomagnification

Case Study: Protecting Children from Toxic Chemicals/Flint Water Crisis lead levels high enough to meet the EPA's definition of "toxic waste.“ 8,657 children exposed to lead by drinking water Flint switched water sources to save money Going to cost $1.5 billion to fix Analysis of umbilical cord blood 180 chemicals found that cause cancers in humans or animals Infants and children more susceptible: Less well- developed immune systems and body detoxification processes Fetal exposure may increase risk of autism, asthma, learning disorders

Scientists Use Live Lab Animals and Non-animal Tests to Estimate Toxicity Mice and rats Systems are similar to humans Small, and reproduce rapidly Dose-response curve – median lethal dose (LD50) Sometimes use the term LC = low concentration (for liquids) More humane methods using animals Replace animals with other models Computer simulations Tissue culture and individual animal cells Chicken egg membranes

Dose-response Curves Nonthreshold dose-response model

There Are Other Ways to Estimate the Harmful Effects of Chemicals Case reports and epidemiological studies Limitations of epidemiological studies Too few people tested Length of time Result linked to chemical Cannot be used for new hazards

Are Trace Levels of Toxic Chemicals Harmful? Insufficient data for most chemicals We are all exposed to toxic chemicals Trace amounts Difference between increasing dangers and better testing

Why Do We Know So Little about the Harmful Effects of Chemicals? Precautionary principle Those introducing a new chemical or new technology need to follow new strategies A new product is considered harmful until it can be proved to be safe Existing chemicals and technologies that appear to cause significant harm must be removed 2000 – global treaty to ban or phase out the dirty dozen persistent organic pollutants (POPs) There are severe limitations in estimating toxicity levels and risks Only 2% of 100,000 chemicals have been adequately tested 99.5% of chemicals used in the United States are not supervised by government

The Greatest Health Risks Come from Poverty, Gender, and Lifestyle Choices Greatest health risk by far Malnutrition, increased infectious disease, unsafe drinking water Gender Being born male Lifestyle choices Overeating, smoking, etc.

Case Study: Death from Smoking Most preventable major cause of suffering and premature death Killed 100 million people during the 20th century Could be linked to increased dementia and Alzheimer’s disease Nicotine – additive

Estimating Risks from Technologies Is Not Easy Reliability System reliability (%) = Technological reliability (%) x Human reliability (%) Human reliability is much lower than technological reliability Much harder to predict Five factors can cause misjudgments in risk: Fear Degree of control Whether a risk is catastrophic or chronic Optimism bias Instant gratification